LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
undercut or recess be left to assure a good fit (figure 27) The workpiece is
then turned to size, stopping the traverse of the cutter bit at the recess.
(d) As in straight turning, the workpiece should be rough turned to
within 1/32 to 1/64 inch of its finished diameter. The procedure described
in the next paragraph should be followed for the finishing cut.
h.
Finish Turning.
(1) General.
When the workpiece has been rough turned to within about
1/32 inch of the finished size, take a finishing cut.
A fine feed, the
proper lubricant, and above all a keen-edged toolbit are necessary to
produce a smooth finish. Measure carefully to be sure that the workpiece is
being machined to the proper dimension.
The lathe should be stopped
whenever measurements are to be made.
(a) f
the workpiece is to be finished to extreme close tolerances, wait
until the
piece is cool before taking the finish cut. If the finished cut
is taken
while the workpiece is still hot and slightly expanded, the
workpiece
will be undersize after it has cooled and contracted.
(b) If the workpiece is to be finished on a cylindrical grinder, leave
the stock oversize to allow enough metal for the grinder to remove.
(c) Perhaps the most difficult operation for a beginner in machine work
is to make accurate measurements. So much depends on the accuracy of the
workpiece that one should make every effort in becoming proficient in the
use of measuring instruments. During the use of the precision tools, one
will develop a certain "feel" through experience.
One should not become
discouraged if their first efforts do not produce perfect results.
To
become proficient in taking measurements, one should practice taking
measurements on pieces of known dimensions, such as gage (Jo) blocks.
(2) Filleted Shoulder Finish.
To finish a filleted shoulder, use
longitudinal feed and turn the small diameter up to the shoulder with a
roundnose turning cutter bit positioned as shown in
62
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